Electrophotography disclosed in U.S. Pat. No. 2,297,691 by Carlson, has been applied to copying machines, printers, etc. Especially, as information processing has been developing rapidly, photoprinters and digital photocopying machines applying electrophotogaphy with a light source of semiconductor laser or light-emitting diode, which is appropriate for digital processing, has become widespread. Accordingly, electrophotographic photoreceptors having a high sensitivity and a good reliability have been required.
So far, inorganic photoreceptors having a photoconductive layer comprising an inorganic photoconductive material such as selenium, zinc oxide, cadmium sulfide, was used as electrophotographic photoreceptors. However, these inorganic photoreceptors dose not satisfy properties such as photosensitivity, durability and safety. Lately, organic photoconductive materials have been actively searched for applying to electrophotography.
In these organic photoconductive materials, polyazo-based pigments, phthalocyanine-based pigments, azulenium salt-based pigments, pyrylium salt-based pigments and naphthoquinone-based pigments have sensitivity to a semiconductor laser light.
However, naphthoquinone-based pigments are disadvantageous in sensitivity and polyazo-based pigments are difficult to synthesize. Regarding azulenium salt-based and pyrylium salt-based pigments, their photoelectric properties are easily deteriorated by moist and their chemical structures are not stable against a strong light such as laser.
Phthalocyanine compounds are widely used as a blue pigment of inks and paints because they are chemically and physically stable. So, they are considered as a charge generating material of electrophotographic photoreceptors. Generally, light absorption spectrum and electric properties of phthalocyanine pigment depend on a kind of its central atom. However, though phthalocyanine compound have the same chemical structure, that is phthalocyanine compounds have the same central atom, the spectrum and electric properties can be varied according to crystal form, crystal habit and particle size.
Till now, many phthalocyanine compounds such as copper phthalocyanine, metal-free phthalocyanine, chloroaluminium phthalocyanine, chloroindium phthalocyanine, chlorogallium phthalocyanine, chlorogermanium phthalocyanine, vanadyloxy phthalocyanine, titanyloxy phthalocyanine, hydroygermanium phthalocyanine, hydroxygallium phthalocyanine, etc. have been proposed as a charge generation material. In these phthalocyanine compounds, phthalocyanine-based charge generation materials having different crystal form include copper phthalocyanine such as ε type copper phthalocyanine, and metal-free phthalocyanine such as X type metal-free phthalocyanine (U.S. Pat. No. 3,357,989), τ type metal-free phthalocyanine (Japanese Patent Application Laying-open No. 62-47054), τ′ type metal-free phthalocyanine (Japanese Patent Application Laying-open No. 60-87332), X type metal-free phthalocyanine (Japanese Patent Application Laying-open No. 60-243089), metal-free phthalocyanine (Japanese Patent Application Laying-open No. 58-182639) and metal-free phthalocyanine (Japanese Patent Application Laying-open No. 2-233769). Titanyl phthalocyanines having different crystal form include α type crystal (Japanese Patent Application Laying-open No. 61-23924), Y type crystal (Japanese Patent Application Laying-open No. 1-17066), I type crystal (Japanese Patent Application Laying-open No. 61-109056), A type crystal (Japanese Patent Application Laying-open No. 62-67094) and C type crystal (Japanese Patent Application Laying-open Nos. 63-364 and 63-366). Otherwise, B type crystal (Japanese Patent Application Laying-open No. 61-23924), m type crystal (Japanese Patent Application Laying-open No. 63-198067) and semi-amorphous type crystal (Japanese Patent Application Laying-open No. 1-123868) were proposed.
As a charge generation materials comprising at least 2 kind of phthalocyanine, a mixture of titanyl phthalocyanine and metal-free phthalocyanine (Japanese Patent Application Laying-open No. 62-194257), X type metal-free phthalocyanine composition crystal comprising titanyl oxy phthalocyanine and metal-free phthalocyanine (Japanese Patent Application Laying-open No. 2-2702067), a composition crystal comprising titanyl phthalocyanine and vanadyl phthalocyanine (Japanese Patent Application Laying-open No. 5-2278), a mixed crystal comprising halogenized potassium phthalocyanine and metal-free phthalocyanine (Japanese Patent Application Laying-open No. 6-234937) and a phthalocyanine composition comprising titanyl phthalocyanine and a halogenized metal phthalocyanine having a trivalent central metal were proposed.
When these phthalocyanine-based charge generation materials are produced, they are roughly agglomerated crystals having a size more than several ten microns. So, they are dispersed in a solvent for atomization and then the dispersed liquid are coated on a photoreceptor substrate. If the particles of dispersed charge generation material become larger due to crystal electric potential, crystal growth, and agglomeration, electrophotographic properties are deteriorated and partial ununiformities of electrical properties during coating process happen. Also, images defects such as black dots and white streaks happen. Accordingly, a charge generation material is required to be stable against crystal transfer, crystal growth, and agglomeration.
However, phthalocyanine-based charge generation materials known to the art have not solved these problems. Y type titanyl phthalocyanine having a highest peak at Bragg diffraction angle (2θ) of 27.3 degree in X ray diffraction spectrum has excellent sensitivity, and thus various crystal forms having different crystal habit have been proposed. However, these crystals are included in II type crystal, which is not stable against solvents as disclosed in Japanese Patent Application Laying-open 62-670094. Accordingly, properties and qualities of the photoreceptor become problematic according to aging. Also, producing cost is expensive due to a bad storing stability.
In the art related to inks and paints, phthalocyanine derivatives have been used to prevent crystal transfer, crystal growth and agglomeration of phthalocyanine pigments. Concretely, copper phthalocyanine having aminomethyl group (Japanese Patent publication No. 39-16787, Japanese Patent Application Laying-open Nos. 47-10831 and 50-21027), sulfonated copper phthalocyanine (U.S. Pat. No. 2,799,595) and copper phthalocyanine having sulfone amide group (U.S. Pat. No. 2,861,005) were proposed. However, these phthalocyanine derivatives cannot be used because they deteriorate electrical properties such as sensitivity and maintenance of electric potential.
In conclusion, though the proposed phthalocyanine-based charge generation materials have a good sensitivity right after dispersed in a solvent, they are not stable in a solvent and their properties become deteriorated according to aging. So, there is needed to develop a controlling agent for preventing crystal transfer in coating solution, a dispersion stabilizer for preventing agglomeration, or a charge generation material having stability against crystallization and agglomeration.
The present invention provides a controlling agent for stabilizing phthalocyanine having a good sensitivity in a solution, and a charge generation material having a good dispersability and stability against crystallization and agglomeration.
Moreover, the present invention provides an electrophotographic photoreceptor having a good sensitivity, electric potential maintenance and image properties.